Denver Broncos / NFL

Analysis: 49ers' quick-hitting runs another worry for Broncos

The Broncos have surrendered at least 121 yards rushing in each of their last four games and are 1-3 in those outings. In the process they have surrendered 20, 31, 24 and 59 points.

And in those four games, opponents have chosen to pound away at the Broncos' bigger defensive fronts — either their base 3-4 or the 4-3 look they used some the last two weeks.

That's to be expected. When an offense lines up with their bigger formations, the defense will respond with their bigger formations.

Against the Titans, the Broncos played their base defense on all but 14 snaps in the game. Against the Ravens, they were in their base defense or short yardage on 52 snaps (including penalties).

Against the Jets, they were in the 4-3 or 3-4 look a combined 50 times. And against Oakland, they were in the 3-4 or 4-3 on 64 snaps combined.

This week, however, they could get an entirely different challenge against the 49ers.

San Francisco running back Frank Gore has good vision, is a patient runner and usually makes good decisions when he makes his move into the line of scrimmage. And the 49ers haven't always been able to block efficiently against the beefier fronts of opposing defenses to give Gore the room he needs.

So, at times they simply choose not to. They run well out of a three receiver look with Gore as the lone running back.

When they line up in three wide, they get a defense's nickel (five defensive backs) or dime (six defensive backs) packages. Usually, one or two linebackers leave the game and will also sub out for smaller defensive linemen who might be better pass rushers.

And the 49ers have made that work well this season. Even in last week's loss against the Panthers, they consistently found room to run when they spread out the Carolina defense.

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The key for the 49ers is they run the bulk of their rushing plays between the guards, they hit it quick and let Gore do the rest once he clears the line of scrimmage. They don't use plays that take time to develop or give the smaller, faster defensive backs time to recover and run the play down.

They've been especially effective against man-to-man coverage because the defensive backs in coverage often have their backs to the line of scrimmage and don't see the handoff out of a passing formation.

And for a run defense that has struggled as much as he Broncos' has, it's just another thing to worry about.

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